This invention relates to a blow pin assembly for use in extrusion blow molding processes to yield thermoplastic containers having a dripless pour lip.
In conventional extrusion blow molding procedures, a hot extruded tube of thermoplastic material is captured between the mold halves of a split blow mold. This capture results in the lower end of the tube being pinched off and a portion of the upper end of the tube extending out of the split blow mold. This upper end of the tube is commonly referred to as a neck moil.
After the tube's capture, a blow pin assembly, which includes a blow pin tip, is lowered so that the tip enters into the tube to forge form the neck finish of the soon to be blown container. Also, neck moil removal procedures are contemporaneously initiated when the tip enters the tube. The neck moil removal is accomplished by providing, as part of the blow pin assembly, a cutter collar designed for making shearing contact with an anvil carried by the split blow mold. Since the neck moil is caught between the cutter collar and the anvil, its separation from the container neck finish is effected. Exemplary of such a blow pin assembly is the one described in U.S. Pat. No. 4,173,447.
Besides removal of the neck moil, the cutter collar and anvil also accomplish another function in that they also form the top and outside edge surfaces of the container lip. Conventionally, the top surface is formed in a plane and the outside edge surface is formed as a sharp corner. While such a lip configuration is widely used, it has a tendency to allow dripping when the liquid contents of the container are poured therefrom.
It has been found that this undesirable dripping can be mitigated by providing a lip which has a rounded top surface. Production of such a lip, however, will require a different apparatus than hereinabove described.
Therefore, it is an object of this invention to provide, for use in the extrusion blow molding of thermoplastic containers, a blow pin assembly which provides a rounded container lip and which effects neck moil removal.